An image forming apparatus such as a copying machine and a printer utilizing an electrophotographic method is provided with an electrophotographic photosensitive member. In such image forming apparatus, the electrophotographic photosensitive member is rotated by a power transmitter, and synchronously with the rotation, operations such as electrification, exposure, development, transfer, and cleaning are repeated, thereby forming an image on a recording medium.
Specifically, in the image forming apparatus, the electrophotographic photosensitive member is electrically charged at its surface and then rotated while being irradiated by laser light for exposure, according to an image pattern, so that an electrostatic latent image is formed on the surface of the electrophotographic photosensitive member. Next, the latent image is developed by attaching toner to the electrophotographic photosensitive member. The toner attached to the electrophotographic photosensitive member is transferred to a recording medium. After the transfer of toner to the recording medium, the electrophotographic photosensitive member is rotated while a cleaning blade is pressed onto the surface of the electrophotographic photosensitive member, so that remaining toner is removed.
The electrophotographic photosensitive member includes a metal cylindrical body on which a photosensitive layer is formed. The photosensitive layer includes a photoconductive layer formed on the cylindrical body and containing inorganic material and a surface layer containing inorganic material to coat the photoconductive layer, and has a constant thickness in the axial direction of the cylindrical body. Here, the constant thickness means that the ratio of a thickness at any portion other than one end of the electrophotographic photosensitive member to a thickness at an end of the electrophotographic photosensitive member the one end is not less than 0.999 and not more than 1.001.
As shown in FIG. 12, an electrophotographic photosensitive member 8 includes an end 80 to which rotation energy is applied by a power transmitter 81, and an end 82 rotatably supported by a bearing flange 83.
The power transmitter 81 includes a power transmitting flange 84 fixed to the electrophotographic photosensitive member 8 and a gear 85 engaging with the power transmitting flange 84. The power transmitting flange 84 is firmly fixed to an inside low portion 86 of the electrophotographic photosensitive member 8 for rotating the electrophotographic photosensitive member 8. On the other hand, the bearing flange 83 allows the rotation of the electrophotographic photosensitive member 8, and not to prevent the rotation, is arranged to have a play (gap) 88 relative to an inside low portion 87 of the electrophotographic photosensitive member 8.
An image forming apparatus 9 is provided with a cleaning blade 90 for removing remaining toner from the electrophotographic photosensitive member 8. As described above, the cleaning blade 90 presses the electrophotographic photosensitive member 8 while the electrophotographic photosensitive member 8 is rotated, thereby removing the remaining toner. Thus, the cleaning blade 90 is attached via urging means such as springs 91 for pressing the surface of the electrophotographic photosensitive member 8.
As described above, the power transmitting flange 84 is firmly fixed to the inside low portion 86 of the electrophotographic photosensitive member 8, while the bearing flange 83 is attached to the inside low portion 87 of the electrophotographic photosensitive member 8 with the gap 88. With such arrangement, when the cleaning blade 90 presses the surface of the electrophotographic photosensitive member 8 for removing the remaining toner thereof, pressing force applied to the end 80 (at the side of the power transmitting flange 84) of the electrophotographic photosensitive member 8 tends to be larger than the pressing force applied to the end 82 (at the side of the bearing flange 83)
As a result, if a foreign object such as dust is caught between the electrophotographic photosensitive member 8 and the cleaning blade 90, the photosensitive layer (the surface layer and the photoconductive layer) is likely to be broken at the end 80 (at the side of the power transmitting flange 84) of the electrophotographic photosensitive member 8 than that at the end 82 (at the side of the bearing flange 83). Especially, when the cleaning blade 90 made of a material having relatively high hardness (JIS hardness of not less than 67 degrees and not more than 84 degrees) presses the surface layer made of a material containing inorganic material with high hardness such as amorphous silicon, the end 82 (at the side of the bearing flange 83) is likely to be broken. If the photoconductive layer of the photosensitive layer is broken and the crack extends to the cylindrical body, electrification charge originally existing on the surface of the photosensitive member moves to the cylindrical body through the crack (providing electrical short circuit), thereby forming a defective image on a recording medium.
The problem may be caused not only when the bearing flange 83 is attached to the inside low portion 87 of the electrophotographic photosensitive member 8 with the gap 88. Specifically, even when a bearing flange (without a shaft) is firmly fixed to the electrophotographic photosensitive member and a shaft is inserted into a through-hole formed at the bearing flange via a bearing, a problem similar to the above-described one may be caused due to a slight play at the bearing.
Patent Document 1: JP-A-6-19230
Patent Document 2: JP-A-2004-239990
Patent Document 3: JP-A-62-272275